Process for the manufacture of dispersible alumino-silicates

ABSTRACT

Process for the manufacture of high-purity alumino-silicates which are dispersible in aqueous and/or aqueous-acidic media by hydrolysis of aluminum compounds and organosilicon compounds

[0001] The present invention relates to a process for the manufacture ofhigh-purity alumino-silicates which are dispersible in aqueous oraqueous-acidic media by hydrolysis of aluminium compounds andorganosilicon compounds.

[0002] There exists a large number and wide variety of naturalalumino-silicates, including many compounds having defined crystallinestructures, such as muscovite, nepheline, and chabasite. When exchangingpart of the silicon atoms in the reticulation of silicates for aluminiumatoms, without destroying the reticulation, zeolites are obtained.

[0003] Besides natural alumino-silicates, there are many syntheticproducts of this kind. Such products may be those defined by crystalchemistry or may be physical mixtures of aluminium hydroxide and silicicacids with different quantities of water. Besides physical mixtures,alumino-silicate defined by crystal chemistry may be present as well.

[0004] A customary process for preparing such alumino-silicates is theconversion of clays, such as kaolin, using silicic acid and sodiumhydroxide. Another synthesis route is the cogelation of aluminiumhydroxide sols with silicic acid sols followed by precipitation [cf. GB2166971-C]. Precipitation of an aluminium salt in a silicic acid sol isknown as well [cf. CA 848966-A].

[0005] The aforesaid processes have the disadvantage that the desiredsols or emulsions only exist at the instant they are prepared, while thepowder obtained by subsequent drying can only incompletely be dispersedor requires solvent mixtures to achieve dispersion. Another disadvantageis that the sols or emulsions prepared in this way contain largequantities of alkali metals or alkaline earth metals used forstabilising the silicic acid. Subsequent purification, e. g. by ionexchange, is incomplete and results in typical concentrations of alkalimetals or alkaline earth metals of 0.1% (equal to 1,000 ppm) afterpurification [cf. US 3,933,6211].

[0006] Heterogeneous catalysis requires high-purity catalyst supportscontaining less than 100 ppm of alkali metals and/or alkaline earthmetals, particularly less than 50 ppm of sodium oxide. The preparationof such high-purity alumino-silicates using ion exchanged ortho-silicicacid is described in German patent DE 38 39 580-C1. The resultantalumino-silicates have the desired high purities, but they cannot bedispersed.

[0007] Alumino-silicates are physically/chemically not comparable withaluminium hydroxides. For instance, their surfaces have higher aciditiesdue to the stronger Lewis acid character of silicic acid. Ibis propertyis utilized for a large number of catalytic processes, such asdesulfurizing, denitrification, oxidation, hydrocracking, and mildhydrocracking.

[0008] Modem catalysts often consist of many different support materials[for instance, cf. GB 2166971-C]. It is essential that the catalystsupport materials be homogeneously mixed to ensure uniform compositions.Therefore, dispersible alumino-silicates offer several advantages, e. g.when used for coating substrates. This method can be used in the fieldof catalysis and materials coating. The explanations given hereinaboveshow that there is a need for dispersible high-purity alumino-silicates.

[0009] It was the object of this invention to develop a synthesis forpreparing dispersible alumino-silicates which offers the followingadvantages:

[0010] Even after drying and conversion into powder, thealumino-silicates prepared according to the present invention shall bedispersible in aqueous solutions without addition of or treatment withorganic solvents.

[0011] The alumino-silicates prepared according to the present inventionshall have high purities.

[0012] The starting materials used for preparing the aforesaid compoundsshall be readily available.

[0013] The Si/Al ratio of the product shall be adjustable by varying theeduct ratio and without using one of the components in excess.

[0014] The price of the starting materials shall allow an economicprocess.

[0015] The manufacturing process shall be feasible both as a continuousand discontinuous process.

[0016] It was surprisingly found that the process described hereinbelowprovides alumino-silicates which solve the problems the presentinvention was based on.

[0017] The instant invention relates to a process for the continuous ordiscontinuous manufacture of high-purity alumino-silicates which can bedispersed in aqueous and/or aqueous-acidic media. The desired propertiesare obtained by the following process:

[0018] Process for the manufacture of alumino-silicates which aredispersible in aqueous and/or aqueous-acidic media wherein

[0019] (A) one or more hydrolyzable aluminium compound(s) and

[0020] (B) one or more hydrolyzable organosilicon compound(s)

[0021] is (are) hydrolyzed. The components are hydrolyzed jointly.Alternatively, they can be hydrolyzed consecutively or separately. Inthe latter case, the (partial) reaction products will be combined afterthe (partial) hydrolysis.

[0022] Hydrolyzable compounds within the meaning of the instantinvention are all the aluminium compounds or organosilicon compoundsforming M—OH and/or M—O—M structures when reacted with water, e. g.organosilicon compounds, such as silicones, alkyl silanes, alkylalkoxysilanes, alkyl halogen silanes, alkoxyhydroxysilanes, or alkylhydroxysilanes, or aluminium compounds, such as aluminium alcoholates,aluminium hydroxy-alcoholates, aluminium oxyalcoholates, aluminiumacetyl acetonates, aluminium alkyl chlorides, or aluminium carboxylates.The hydrolysis may be carried out at 20 to 98° C., preferably 50 to 98°C., most preferably 85 to 98° C.

[0023] Preferably, compounds of the type M(O—R—A—R′)_(z-n) (O—R″)_(n)are employed, wherein independent of each other and, optionally,different for each residue

[0024] M is aluminium or silicon,

[0025] R″, is a branched or an unbranched, a cyclic or an acyclic, or anaromatic hydrocarbon residue having 1 to 30, particularly 2 to 12 carbonatoms,

[0026] R′ is a branched or an unbranched, a cyclic or an acyclic, or anaromatic hydrocarbon residue having 1 to 10 carbon atoms, particularlyan alkyl residue having 4 to 8 carbon atoms,

[0027] R is a bivalent and branched or unbranched, cyclic or acyclic, oraromatic C₁ to C₁₀ hydrocarbon residue, particularly an alkyl residuehaving 1 to 5 carbon atoms, most preferably 1 to 3 carbon atoms, thelatter one most preferably being unbranched and acyclic,

[0028] A represents a heteroatom of main group 6 (oxygen group) or maingroup 5 (nitrogen group) of the periodic system, preferably oxygen ornitrogen, wherein, if A represents an element of main group 5, A bearshydrogen or a C₁ to C₁₀ alkyl residue or a C₆ to C₁₀ aryl-/alkyl arylresidue as additional substituent(s) for the saturation of its valences,and

[0029] n is an index for the numbers 0, 1, 2, or 3 if M is aluminium, oris an index for the numbers 0, 1, 2, 3, or 4 if M is silicon, and

[0030] z is an index for the number 3 if M is aluminium, or is an indexfor the number 4 if M is silicon.

[0031] Preferably, n is equal to 0 or equal to 3 if M is aluminium. If Mis silicon, n is preferably equal to 4. If n is equal to 0 and A isoxygen, metal trisbuty-lene glycolates are preferred. It is preferredthat M be aluminium.

[0032] In case n is equal to 3, the aluminium compounds are aluminiumtrisalco-holates which, with increasing preference, have C₂ to C₁₂, C₄to C₈, or C₆ to C₈ hydrocarbon residues, the residues being saturated orunsaturated, cyclic or acyclic, branched or unbranched, or aromatic,preferably saturated. Saturated, linear C₆ to C₈ hydrocarbon residuesare particularly preferred. For example, hydrolyzable aluminiumalcoholates may be prepared according to the process disclosed in EP 011 1 115-A1.

[0033] In case n is equal to 4, the hydrolyzable organosilicon compoundsare silicon alcoholates. Preferred silicon alcoholates have C₁-C₈hydrocarbon residues, the residues being saturated or unsaturated,cyclic or acyclic, branched or unbranched, or aromatic. Saturated C₂ toC₄ hydrocarbon residues are particularly preferred.

[0034] Furthermore, the process according to the instant invention issuperior by the fact that, apart from the educts or products, thereaction can be carried out without any organic solvents and in anessentially aqueous or alcoholic/aqueous environment.

[0035] According to an embodiment of the present process, thehydrolyzable organosilicon compounds are prehydrolyzed or partiallyhydrolyzed prior to addition of the hydrolyzable or hydrolyzed aluminiumcompound with 0.5 to 3 moles of water, preferably 1 to 2 moles, per moleof silicon, i.e. less than the stoichiometric amount. Said partialhydrolysis is preferred, whenever the hydrolyzable aluminium compound isnot of the type Al(O—R—A—R′)_(3-n) (O—R″)3.

[0036] Prior to use, the hydrolyzable metal compounds may be purified bydistillation, filtration, ion exchange and/or centrifugation.

[0037] In addition, dispersibility improves by several percent when thecombined reaction products of the silicon and aluminium compounds aresubjected during or after the hydrolysis to joint hydrothermal treatmentin an aqueous environment at temperatures of 40 to 220° C. for a periodof greater than 0.5 hour. In another embodiment of this process thehydrothermal ageing is performed during a period of 0.5 to 24 hours.Preferably, the treatment is performed at temperatures of 80 to 130° C.for a period of 1 to 20 hours, most preferably 5 to 20 hours.

[0038] Optionally, an acid may be present during the hydrothermaltreatment. It is preferred that this acid be a monovalent organic C₁ toC₆ acid or a mono-valent inorganic acid (a monovalent mineral acid),such as HCl or HNO₃. The acid may also be added after the hydrolysis,but it should be added before drying and should be present during thehydrothermal treatment.

[0039] It can be used in quantities of 0.1 to 2.0 grams, preferably 0.2to 0.8 gram, referring to 1 gram of solid material.

[0040] Within the meaning of the present invention, monovalent organicC₁ to C₆ acids are organic compounds which have at least 1 to 6 carbonatoms and show an acid reaction in the presence of water, i.e. react asproton donators, and which can set free only one proton, referring tothe acid molecule. This definition includes for instance acid chlorides,sulfonic acids, and other organic compounds forming —COOH or —COO⁻groups in water.

[0041] The educts may be used in quantities of from 99.5 wt. %:0.5 wt. %to 50 wt. %:50 wt. %, preferably from 98 wt. %:2 wt. % to 50 wt. %:50wt. %, each referring to the ratio of Al₂O₃:SiO₂. Bases, such as ammoniasolution, may be added after the hydrolysis in order to achieve betterseparation of the organic phase. Furthermore, the reaction product ofthis invention can be calcined at temperatures of 550° C. to 1,500° C.for a period of 0.5 hour to 24 hours.

[0042] The dispersible alumino-silicates are useful as catalysts,catalyst supports for catalytic processes, for the manufacture ofcatalysts, as starting materials for ceramics, as coating materials, andas binder components and rheo-logical modifiers in aqueous systems.

[0043] The term ‘dispersible alumino-silicates’ as used in the presentinvention means dry and, most expediently, powdery alumino-silicateswhich can be dispersed in aqueous media in quantities of at leastgreater than 90 wt. %, preferably greater than 95 wt. %, i.e. greaterthan 90 wt. %. preferably greater than 95 wt. % of said products willremain dispersed after dispersion. In the experimental part describedhereinbelow a method for quantifying the dispersibility is described.The resultant aqueous products can be dried using known methods, such asspray drying or by means of a rotary drier. The process formanufacturing alumino-silicates according to this invention can becarried out continuously or discontinuously.

[0044] The alumino-silicates of this invention can be dispersed usingwater-diluted acids, such as inorganic acids, e. g. hydrochloric acid,nitric acid, or C₁ to C₆ organic acids, monovalent acids beingpreferred. The acids used for dispersion can be employed inconcentrations of 0.1 to 40 wt. %, referring to the straight acid.Preferably, lower concentrations are used, i. e. from 0.1 to 5 wt. %. Insome cases it is also possible to use only water for dispersion.

[0045] The compounds manufactured according to this invention can becalcined in a furnace at temperatures of 550° C. to 1,500° C. for aperiod of 3 to 24 hours. The metal oxide manufactured in this way hasthe requisite high purity.

[0046] Table 1, following, shows several alumino-silicates manufacturedaccording to the present invention and their dispersibilities D. TABLE 1Al₂O₃:SiO₂ HNO₃ Ageing Dispersibility D Compound [wt. %] [wt. %] [h/°C.] [%] 1 72.3:27.7 30.0 — 96 2 61.5:38.5 25.0 — 96 3 72.3:27.7 2.0 16h/95° C. 97 4 51.6:48.4 30.0 — 95 5 95.0:5.0 0.8 16 h/95° C. 97 674.1:25.9 30 — 98 A 95.1:4.9 30 — nondispersible B 50.4:49.6 30 —nondispersible C 68.8:31.2 30  5 h/95° C. nondispersible

[0047] Table 2, following, shows the physical data of thealumino-silicates according to this invention in comparison with twostandard alumino-silicates (A and B). The reference alumino-silicates Aand B were prepared by mixing an alumina sol with silicic acid. TABLE 2Al₂O₃:SiO₂ Surface Pore Volume Compound [wt. %] [m²/g] [ml/g] 172.3:27.7 426 0.41 2 61.5:38.5 406 0.35 3 72.3:27.7 315 0.22 4 51.6:48.4303 0.31 5 95.0:5.0 527 0.73 6 74.1:25.9 500 0.62 A 95.1:4.9 314 0.54 B50.4:49.6 452 0.60

[0048] The dispersible alumino-silicates manufactured according to thisinvention have high purities. In particular, the content of alkalimetals and alkaline earth metals which have particularly adverse effectswhen using the aforesaid products for catalysis is very low. The resultsof the trace elements analysis by ICP spectroscopy are listed in Table3. The purities listed in Table 3 can be further increased by usingbidistilled water and containers made of inert materials. TABLE 3 Na₂OLi₂O MgO CaO TiO₂ Fe₂O₃ Compound [ppm] [ppm] [ppm] [ppm] [ppm] [ppm] 113 <5 <10 <10 <50 12 2 <10 <5 <10 <10 <50 48 4 16 <5 <10 <10 <50 63 5<10 <5 <10 <10 <50 28 6 12 <5 <10 <10 <50 35 # Mn, Mo, and Ga, is lessthan 50 ppm in total.

EXAMPLES (General)

[0049] The compounds prepared according to this invention were analysedfor trace impurities by inductively coupled plasma (ICP) spectroscopy.The surfaces were determined by the BET method, while the pore volumeswere additionally determined by mercury porosimetry (Autopore II 9220porosimeter. Mikromeritics) and nitrogen porosimetry (Flow Prep 060,Gemini 2360, 2375, Mikromeritics). The compounds of this invention werecalcined in a muffle furnace at temperatures of between 550° C. and1,500° C. Deionised water was used for the hydrolysis.

[0050] The dispersibility D was determined by the following method. Acertain amount of the dry, solid material was placed into a beaker andmixed with dilute acid, e. g. nitric acid, while stirring. Stirring wascontinued for 10 minutes (stirrer speed 800-850 rpm). The suspensionthus obtained was quantitatively transferred to the glass tube of acentrifuge. Subsequent to centrifugation for 20 minutes at 2,400 rpm⁻¹,the supernatant was decanted, and the residue in the glass tube wasdried for at least 0.5 hour at 573 K (300° C. ). The glass tube then wasweighed including the residue, and there-after without residue. Thedifference obtained is the weight of nondispersed solid.$\text{Nondispersed quantity, \%} = \frac{\text{gram of residue} \times 100}{\text{initial weight of alumina, in grams}}$Dispersed quantity D, % = 100 − percentage of nondispersed quantity

[0051] Example 1 (Compound 1)

[0052] Into a 1,000-ml three-neck flask, there were placed 136.4 gramsof silicon tetraethanolate (14.25 wt. %). The contents was heated to 90°C. Addition of 11.8 grams of 1% nitric acid resulted in moderateprecipitation. After stirring for 1 hour, 400 grams of aluminiumtrishexanolate (6.3 wt. %) were added. Then, this mixture was added inthree portions to 686 grams of water heated to 90° C. in order toperform the hydrolysis. Hydrolysis took 1 hour. During this period,after 40 minutes, 8.4 grams of 25% ammonia solution were added tofacilitate phase separation. The supernatant alcohol was decanted andthe remaining aqueous phase was liberated from alcohol residue by steamdistillation, followed by spray drying.

[0053] Example 2 (Compound 2)

[0054] Into a 1,000-ml three-neck flask, there were placed 212 grams ofsilicon tetra-ethanolate (14.25 wt. %). The contents was heated to 90°C. Addition of 18.4 g of 1% nitric acid resulted in moderateprecipitation. After stirring for 1 hour, 400 grams of aluminiumtrishexanolate (6 wt. %) were added. Then, this mixture was added inthree portions to 778 grams of water heated to 90° C. in order toperform the hydrolysis. Hydrolysis took 1 hour. During this period,after 40 minutes, 9.6 grams of 25% ammonia solution were added tofacilitate phase separation. The supernatant alcohol was decanted andthe remaining aqueous phase was liberated from alcohol residue by steamdistillation, followed by spray drying.

[0055] Example 3 (Compound 3)

[0056] Into a 1,000-ml three-neck flask, there were placed 179 grams ofsilicon tetra-ethanolate (14.25 wt. %). The contents was heated to 90°C. Addition of 15.5 g of 1% nitric acid resulted in moderateprecipitation. After stirring for 1 hour, 500 grams of aluminiumtrishexanolate (6.3 wt. %) were added. Then, this mixture was added inthree portions to 883 grams of water heated to 90° C. in order toperform the hydrolysis. Hydrolysis took 1 hour. After addition of 8.5grams of HNO₃ (65 wt. %), ageing was performed at 95° C. for 16 hours.The supernatant alcohol was decanted and the remaining aqueous phase wasliberated from alcohol residue by steam distillation, followed by spraydrying.

[0057] Example 4 (Compound 4)

[0058] Into a 1,000-ml three-neck flask, there were placed 318 grams ofsilicon tetra-ethanolate (14.25 wt. %). The contents was heated to 90°C. Addition of 27.5 g of 1% nitric acid resulted in moderateprecipitation. After stirring for 1 hour, 400 grams of aluminiumtrishexanolate (6.3 wt. %) were added. Then, this mixture was added inthree portions to 870 grams of water heated to 90° C. in order toperform the hydrolysis. Hydrolysis took 1 hour. During this period,after 40 minutes, 11 grams of 25% ammonia solution were added tofacilitate phase separation. The supernatant alcohol was decanted andthe remaining aqueous phase was liberated from alcohol residue by steamdistillation, followed by spray drying.

[0059] Example 5 (Compound 5)

[0060] In a 1,000-ml three-neck flask, there were mixed 550 grams ofaluminium trisbutylene glycolate (Al content 5.6 wt. %) and 21.4 gramsof silicon tetra-ethanolate (14.25 wt. %). This mixture was added inthree portions to 735 g of water and 6.2 g of HNO₃ (65 wt. %) heated to75° C. in order to perform the hydrolysis. Hydrolysis took 1 hour. Afterphase separation, the supernatant organic phase was decanted. Theaqueous phase was heated to 95° C. and maintained at this temperaturefor 16 hours. The alcohol in the aqueous phase was eliminated by steamdistillation, followed by spray drying.

[0061] Example 6 (Compound 6)

[0062] In a 1,000-ml three-neck flask, there were mixed 200 grams ofaluminium trisethylglycolate (Al content 6.8 wt. %) and 38.6 grams ofethyl glycol with 38.6 grams of silicon tetraethanolate (28.5 wt. %).This mixture was added in three portions to 360 g of water heated to 30°C. in order to perform the hydrolysis. Hydrolysis took 1.5 hours. Then,4.4 grams of 25% ammonia solution were added. After phase separation,the supernatant organic phase was decanted. The alcohol in the aqueousphase was eliminated by steam distillation, followed by spray drying.

[0063] Example 7 (Comparative Example Compound C)

[0064] Into a 2,000-ml three-neck flask, there were placed 638 grams ofaqueous silicic acid. The contents was heated to 75° C. A total of 500grams of aluminium trishexanolate (Al content 6.35 wt. %) were added inthree portions at time intervals of 15 minutes. After stirring for 30minutes, the alcohol was decanted and the residue was diluted to asolids content of 5%. The sol was heated to 95° C. and maintained atthis temperature for 5 hours. The remaining aqueous phase was liberatedfrom alcohol residue by steam distillation, followed by spray drying.

1. A process for the manufacture of alumino-silicates which aredispersible in aqueous and/or aqueous-acidic media, characterised inthat one or more hydrolyzable aluminium compound(s) and one or morehydrolyzable organosilicon compound(s) are hydrolyzed jointly ordiscontinuously in space or time.
 2. A process according to claim 1,characterised in that the hydrolyzable compounds of claim 1 arecompounds of the type M(O—R—A—R′)_(z-n) (O—R″)_(n), wherein independentof each other M is aluminium or silicon, R″ is a hydrocarbon residuehaving 1 to 30 carbon atoms, R′ is a hydrocarbon residue having 1 to 10carbon atoms, R is a bivalent hydrocarbon residue having 1 to 10 carbonatoms, and A represents a heteroatom of main group 6 (oxygen group) ormain group 5 (nitrogen group) of the periodic system, preferably oxygenor nitrogen, wherein, if A represents an element of main group 5, Abears hydrogen or a C₁ to C₁₀ alkyl residue or a C₆ to C₁₀ aryl-/alkylaryl residue as additional substituent(s) for the saturation of itsvalences, and n is an index for the numbers 0, 1, 2, or 3 if M isaluminium, or is an index for the numbers 0, 1, 2, 3, or 4 if M issilicon, and z is an index for the number 3 if M is aluminium, or is anindex for the number 4 if M is silicon.
 3. A process according to claim2, characterised in that n is equal to
 0. 4. A process according toclaim 2, characterised in that n is equal to 3 if M is aluminium and/orn is equal to 4, if M is silicon.
 5. A process according to any one ofclaims 1, 2, or 4, characterised in that silicon alcoholates having C₁to C₈ hydrocarbon residues, preferably saturated C₂ to C₄ hydrocarbonresidues, are used as hydrolyzable silicon compounds.
 6. A processaccording to any one of the preceding claims, characterised in that,prior to addition of the hydrolyzable aluminium compound, thehydrolyzable silicon compounds are prehydrolyzed with water or diluteacid using 0.5 to 3 moles of water, preferably 1 to 2 moles, per mole ofsilicon, i.e. less than the stoichiometric amount.
 7. A processaccording to any one of the preceding claims, characterised in thataluminium alcoholates having C₂ to C₁₂, preferably C₄ to C₈, mostpreferably saturated C₆ to C₈ hydrocarbon residues are used ashydrolyzable aluminium compounds.
 8. A process according to any one ofthe preceding claims, characterised in that the hydrolysis is performedat 20 to 98° C., preferably 85 to 98° C.
 9. A process according to anyone of the preceding claims, characterised in that during or after thehydrolysis the reaction products of claim 1 are jointly subjected tohydrothermal ageing in an aqueous environment at temperatures of 40 to220° C. for a period of greater than 0.5 hour.
 10. A process accordingto claim 9, characterised in that the hydrothermal ageing is conductedfor a period of 0.5 hour to 24 hours, preferably 1 to 20 hours.
 11. Aprocess according to any one of claims 9 or 10, characterised in thatthe hydrothermal ageing is conducted at 80 to 130° C.
 12. A processaccording to any one of claims 9 to 11, characterised in that thehydrothermal ageing is conducted in the presence of acid.
 13. A processaccording to claim 12, characterised in that the acid is added after thehydrolysis, but prior to hydrothermal treatment.
 14. A process accordingto any one of the preceding claims, characterised in that the acid whichis present during or after the hydrolysis is a monovalent organic C₁ toC₆ acid or a monovalent mineral acid.
 15. A process according to any oneof the preceding claims, characterised in that the hydrolyzable metalcompounds were previously purified by distillation, filtration, orcentrifugation and/or are liberated from metal ions by ion exchange. 16.A process according to any one of the preceding claims, characterised inthat the aluminium compound/silicon compound ratio is from 99.5 wt. %:0.5 wt. % to 50 wt. %:50 wt. %. each referring to Al₂O₃ and SiO₂.
 17. Aprocess according to any one of the preceding claims, characterised inthat the reaction product of the invention is calcined at temperaturesof between 550° C. and 1,500° C. for a period of 0.5 hour to 24 hours.18. Tie use of the alumino-silicates manufactured according to theprocess defined in the preceding claims as catalysts, catalyst supports,for the manufacture of catalysts, as starting materials for ceramics, ascoating materials, and as binder components and/or rheological modifiersin aqueous systems.
 19. The alumino-silicates manufactured according toany one of the processes defined in claims 1 to
 17. 20.Alumino-silicates dispersed in aqueous or aqueous/alcoholic media,characterised in that the alumino-silicate is manufactured according toany one of the processes defined in claims 1 to
 17. 21. Thealumino-silicates dispersed in aqueous or aqueous/alcoholic mediaaccording to claim 20, characterised in that the alumino-silicate, priorto dispersion in the aqueous or aqueous/alcoholic medium, is present ina dried, essentially anhydrous state.